In the link it has his letter to his British publisher, where he was even more blunt. Maybe the first time that "I have _______ friends" has actually rung true.

Personally, I should be inclined to refuse to give any Bestätigung (although it happens that I can), and let a German translation go hang. In any case I should object strongly to any such declaration appearing in print. I do not regard the (probable) absence of all Jewish blood as necessarily honourable; and I have many Jewish friends, and should regret giving any colour to the notion that I subscribed to the wholly pernicious and unscientific race-doctrine.